Study On Toxic Effects Of Dichromate On Two Crop Species

This thesis examined toxic effect of heavy metal chromium on the seedlings of crop plants of naked oat (Avena sativa) and Sorghum (Sorghum vulgare). Each plant was exposed to the potassium dichromate solution of different concentration for cultivation. The exposes were performed in two ways:1) exposure starting from the8-day seedlings at the concentrations of Omg/1,20mg/l,50mg/l, and80mg/l; and2) exposure starting from seed germination at the concentrations of0mg/l,5mg/l,10mg/l, and15mg/l. During the period of exposure the roots and stems were measured for growth inhibition. At the end of exposure the physiological parameters were tested as follows:chlorophyll a and β, malondialdehyde, root activity, relative protein contents, and Cr6+accumulation. The comparisons were made using ANOVA and the results are summarized.For both species the Cr6+concentration were positively correlated with the inhibition of growth in both stem and root. At low concentration such inhibition increased with the time, especially at later stage. The root was more damaged than stems and the older seedlings were more resistant than germinating seedlings. For sorghum the chlorophyll a was found more resistant to Cr6+than chlorophyll β; and naked oat was found tolerant to Cr6+at50mg/l, at least to certain extent. When Cr6+is below15mg/l no notable inhibition of chlorophyll was observed. For seedlings exposed to at high Cr6+concentration of80mg/l the oxidation damage was observed in sorghum but not in naked oat. However the germinating seedlings were found severely damaged to Cr6+at concentration as low as10mg/l. The overall resistance of naked oat seedlings was found higher than that of sorghum. It was noted that the low Cr6+concentration (20mg/l) stimulated the sorghum root activity. In contrast the root activity was inhibited at the concentration of80mg/l for both crops. The Cr6+exposure had significant effects on relative protein contents of germinating seedlings of sorghum, and for naked oat such effects were observed at Cr6+concentration of15mg/l. It was observed that sorghum accumulates more Cr6+than naked oat. The Cr6+concentration in root is much higher than in stem. Being the main organ for Cr6+accumulation root was and therefore more damaged. The tolerance of seedlings was higher than those at germinating stage.This study indicated the correlation of Cr6+toxicity and tolerance in two crop species, as evident in differential responses of the morphological and physiological parameters to the acute exposure. The results provided the basic toxicological data of the chromium for crops commonly seen in loess plateau with implications of using both crops for phyto-remediation of contaminated soil.